Electric fuse having improved cap link connection



June 18, 1953 F. J. KozAcKA 3,094,600

ELECTRIC FUSE HAVING IMPROVED CAP LINK CONNECTION Filed Dec. l, 1960 3 Sheets-Sheet 1 June 18, 1963 F. J. KozAcKA ELECTRIC FUSE HAVING IMPROVED CAP LINK` CONNECTION 5 Sheets-Sheet 2 Filed Dec.

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United States Patent O 3,094,600 ELECTRIC FUSE HAVING llVIPROVED CAP LINK CONNECTION Frederick J. Kozacka, Amesbury, Mass., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Dec. 1, 1960, Ser. No. 72,945 4 Claims. (Cl. 200-132) This invention relates to electric fuses, and more particularly .to electric cartridge fuses.

It is a general object of this invention to generally improve fuses of this description.

-Fuses having tubular `fuse links have a large area of intimate coaction between the fusible element or fuse link and the surrounding pulverulent arc-quench filler. For this reason `fuses having tubular fuse links tend to have a large interrupting capacity. Fuses having tubular fuse links tend also to have an appreciable time lag when blowing under overload condition, as distinguished from short-circuit conditions.

It is, therefore, a special object of this invention to provide improved electric fuses hav-ing tubular links and combining high interrupting capacity for clearing short-circuit currents 4with time lag to prevent premature blowing on inrush currents and permissible overload currents.

My United States Patent 2,777,033, Jan. 8, 1957, for Power Fuses With Tubular `Links and Pressure-type Link Connections, is concerned with a fuse of the above character. The structure disclosed in that patent includes terminal elements in the form of copper plugs which are press-fitted into the ends of. the tubular casing and annular pressure type link connections. These fuses exhibit desirable operating -characteristics ibut the manufacturing costs thereof are relatively high.

It is, therefore, another object of this invention to provide :fuses having substantially the same operating or performance characteristics as those disclosed in the aforementioned patent, but involve smaller manufacturing cost than the latter.

This is a continuation-in-part of my copending patent application Ser. No. 627,624, tiled December ll, 1956, now abandoned, for Manufacturing Cartridge Fuses.

It is a special object of this invention to provide improved fuses predicated upon the application of the method or process disclosed in my aforementioned patent application Ser. No. 627,624.

A further object of this invention is to provide fuses having minimal departures from the time-current curve thereof or, in other words, fuses having minimal manufacturing tolerances affecting the time-current curve of the particular type of fuses.

It is still another object of the invention to provide improved cartridge fuses comprising solder joints between the caps or ferrules and the ends of the fusible element which solder joints are situated entirely inside of the fuse.

These and other objects of the invention and advantages thereof will become more apparent from the following description of several preferred embodiments of the invention when taken in connection with the accompanying drawings wherein:

FIG. l is a longitudinal section of a first embodiment of the invention taken along 1-1 of FIG. 2;

FIG. 2 -is a longitudinal section of the structure shown in FIG. l taken along 2--2 of FIG. l;

FIG. 3 is a section Itaken along 3-3 of FIG. l showing a detail of the structure on a larger scale;

FIG. 4 is a section similar to that shown in FIG. 3 and illustrates a structural change in the detail shown resulting from the application of a resilient material for the fuse tube or casing;

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FIG. 5 shows the same structure as FIG. 4 upon establishment of a solder joint between the fuse link and the cap or ferrule;

FIG. 6 is a section taken along y6--6 of FIG. l and showing a detail of the structure on a larger scale;

il-TIG. 7 shows another embodiment of the invention comprising -a tubular fuse link and is a section along 7 7 of FIG. 8;

FIG. 8 refers to the structure shown in lFIG. 7 and is a longitudinal section across one end of a cartridge fuse having a relatively high current-carrying capacity and is taken along 8 8 of FIG. 7;

FIG. 9 is a longitudinal section showing the top end of a fuse before completion of the assembly process, the f-use having a relatively rigid or non-resilient casing; and

FIG. l0 shows the same structure as FIG. 9 upon completion of the assembly process.

Referring now to the drawings, and more particularly to FIGS. 1 and 2 thereof, .the -multiperforated ribbontype fuse link 1 of copper or silver having an overlay of tin adjacent the center thereof is arranged in a tubular casing 2 of insulating material. Casing 2 is filled with a pulverulent arc-quenching ller 3 as, for instance, quartz sand. Under certain circumstances which will -be dealt with below more in detail it may be useful, or necessary, to use another pulverulent filler instead of quartz sand. The axially outer ends of casing or fuse tube 2 form a pair of circular rims 2a, 2a. Ribbon-link' 1 has points engaging angularly displaced points of the pair of rims 2a, 2a, i.e. points of rims 2a, 2a which are displaced 180 degrees. The axially outer ends 1a of link 1 are bent Yaround the points of rims 2a, 2a engaged by link 1 to the outer surface of casing 2. A pair of metal caps 6, 6 closes the axially outer ends of `casing 2. Caps 6 have substantially flat circular inner surfaces 6a and substantially cylindrical inner lateral surfaces 6b. The caps 6 are pressure-mounted on casing 2t and the axially inner ends thereof are crimped into casing 2 for increased mechanical strength of the structure. Reference numerals 5, 5 have been applied to indicate a pair of pools or a pair of layers of soft solder substantially coextensive with the ilat circular inner Isurfaces 6a. of caps 6. The solidified pools or layers 5 of soft solder have projections 5a, 5a extending in a direction longitudinally of casing 2 into gaps G formed between casing 2 and caps 6i, 6. These projections establish solder joints between the inner cylindrical lateral surfaces 6b of caps 6 and the ends 1a of ribbon link 1 situated on the outer surface of casing 2. In order to establish the co-mposite solder joints and projections 5, 5a a circular solder-flux-solder lamination may be introduced into caps 6, whereupon the caps are heated to the fusing point of the constitutent solder of the aforementioned laminations. Laminated material comprising outer layers of soft solder sandwiching an inner layer of lflux are commercially available. Circular stampings may readily be made from such a solder-fluxsolder lamination and placed into caps 6' in registry with the surfaces 6a thereof. The method of manufacturing solder joints of the aforementioned character by means of solder-ilux-solder laminations is described in considerable deta-il in my aforementioned copending patent application Ser. No. 627,624, and reference may be had to that application for further details concerning the manufacturing method.

When the solder sandwich which is coextensive with cap surface 6a melts under the heat applied to, or generated in, cap `6, the solder establishes a first solder joint or primary solder joint which is situated exactly at the point of fuse link 1 engaging rims 2a, 2a. If the material of which casing 2 is made were soft, and entirely non-resilient or plastic, the fuse link 1, or the ends 1a thereof would be 3 pressed by caps 6 into the casing material, as illustrated in FIG. 3. yIf the material of which casing 3 :is made is relatively resilient, the casing 2 is elastically deformed by cap 6 and link 1 as shown in FIG. 4, thus forming lateral cavities G in the outer surface of casing 2 situated to both sides of each of ribbon-link 1. Upon fusion during the manufacturing process of the circular laminated solder stamping, the constituent fused liquid solder is drawn by capillary action into the afore-mentioned lateral cavities G (FIG. 4), resulting in the formation of the secondary solder joints or projections 5a. The latter carry little or no current since they are shunted out by the primary solder joints 5 formed at the points where link 1 is bent around rims 2a, 2a. The secondary solder joints Sa extending in a direction longitudinally of casing 2 help to abstract heat from link 1, and form an additional safety feature in case that the primary solder joint 5 between the caps 6 and the link 1 at the point where the latter is bent around rims 2a, 2a should be defective, for one reason or another. Production controls reveal, however, that primary solder joints 5 are virtually never defective.

I have found that the formation of lateral cavities G to both sides of each end of fuse link 1 is particularly satisfactory if the casing 2 is made of a synthetic rubber or, to be more specific, of an acrylonitrile-butadiene-Styrene copolymer. The use of such material in the design of electric fuses has been treated in the copending patent application of Kenneth W. Swain and Harry H. Hallas, iiled November 14, 1960, Ser. No. 68,828, now Patent No. 3,010,000, for Fusible Protective Devices, and reference may be had to that application for further information as to the precautions that must be taken if acrylonitrile-butadiene-Styrene copolymers are used for making casing 2.

Referring now to FIGS. 7 and 8, numeral 2 has been applied to designate a casing of relatively iiexible insulating material as, for instance, the aforementioned acrylonitrile-butadiene-styrene copolymer. The casing 2' forms a pair of rims 2a at the axially outer ends thereof of which but one appears in FIGS. 7 and 8. The substantially tubular fusible element 1 of a resilient sheet metal, e.g. copper, is arranged in coaxial relation to, and inside of, casing 2. Fusible element 1' may be formed by bending a piece of resilient sheet copper around a cylindrical mandrel, thus imparting to it a more or less tubular shape. Fusible element 1 has an axially inner substantially cylindrical portion 1c' and a pair of axially outer portions 1d' substantially in the shape of frustrated cones. Reference character 1f has been applied to indicate perforations of cylindrical portion 1c and reference character o indicates an overlay of tin on cylindrical portions 1c'. FIG. 8 shows but one of the axially outer portions 1d in the shape of a frustrated cone; the other such portion situated adjacent the opposite end of the casing or fuse tube 2 is identical to that shown in FIG. y8. Both portions 1c' and 1d are arranged in coaxial relation to casing 2' and the axially outer portions 1d have angularly displaced substantially V-shaped slots 1m' extending in a `direction longitudinally of casing 2 and forming a plurality of angularly displaced equidistantnly spaced terminal strips 1g', Terminal strips 1g engage angularly displaced equidistantly spaced points of rims 2a and have ends 1a' bend around said points of rims 2a to the outer surface of casing 2. A pair of nietal caps 6 (of which but one is shown in FIGS. 7 and 8) closes the axially outer ends of casing 2. Each metal cap 6' has a substantially flat circular inner end surface 6a and a substantially cylindrical inner lateral surface 6b. Each cap `6 further comprises a pair of blade contacts 7' for inserting the fuse into an electric circuit. Blade contacts 7' form an integral part of caps 2', i.e. they are iixedly secured to them as, for instance, by brazing or rivetting. A layer 5' of soft solder is interposed between the liat inner surface 6a of each cap G' and said plurality of terminal strips 1g at the point thereof engaging rims 2a'. This layer 5' of soft solder is iigures other than FIGS.

a means for establishing a current path of small resistance between ribbon link 1 and blade contacts 7. Each layer 5' has projections 5a extending in a direction longitudinally of casing 2 into gaps G formed between casing 2 and caps 6 and establishing solder joints between the ends `of terminal strips 1g on the outer surface of casing 2' and the cylindrical lateral surfaces 6b of caps 6'. Projections 5a are means for increasing the area of heat exchange between tubular ribbon link 1' and caps 6. The projections 5a' are shunted out by solder joints 5', i.e. the current -iiows directly from tubular link 1 through the fiat end surfaces 6a' of caps 6 to blade contacts 7, and parts la, 5a' hardly perform any current-carrying duty. The main purpose of soft solder projections 5a is to carry heat from the link 1' to caps 6 from where it is dissipated into space.

The operation of this structure can best be understood when realizing that the configuration of the electric eld and that of the temperature tield are very different in the structure of FIGS. 7 and 8. The pattern of the lines of current ow through caps 6 to blade contacts 7 is determined by the configuration of the electric iield, i.e. the voltage gradients along the axially outer ends of links 1', along caps 6 and along blade contacts 7. The voltage gradient in these parts cause the current to liow from link 1 directly from the points of link 1 engaging surfaces 6a to blade contacts 7 without reversing its direction and flowing through the lateral portions of caps 6. There is, however, a significant temperature gra-dient between the ends of strips 1g' on the outer surface of casing 2 and the lateral surfaces of caps `6' causing a ilow of heat from strips -1g' into said lateral surfaces.

Referring now to EFIGS. 9 and 10, numeral 2" has been applied to indicate a casing of an insulating material which is not resilient, eig. a casing of a synthetic-resinglass-cloth laminate. Casing 2" forms a pair of circular rims 2a at the axially outer ends thereof of which but one is illustrated in FIGS. 9l and 10. An elongated fusible element 1" formed by a length of perforated resilient sheet metal ribbon, preferably copper ribbon, is inserted into casing 2". Ribbon 1 has points engaging points of rims 2a angularly displaced 180 degrees, but only one such point has been' shown in FIGS. 9 and 10, this detail 'having been fully illustrated in FIGS. 1 and 2. The axially outer ends 1a of ribbon 1" are bent around the points of rims 2a engaged by rib-bon 1 to the outer surface of casing 2". A pair of metal caps 6 having an inner diameter substantially exceeding the outer diam. eter of casing 1l are mounted upon the axially outer ends of casing 2". Caps 6" have iiat circular inner end surfaces 6a and cylindrical inner lateral surfaces 6b". Caps 6" and casing 2 jointly define a relatively wide intermediate gap G therebetween. Due to their resiliency the ends 1a" of link 1'l have a tendency to turn' radially outwardly into firm engagement with the lateral inner surface of caps 2". This tendency is also present in the other embodiments of the invention illustrated in 9 and 10, but is particularly of FIGS. 9 and 10 because of the relatively large width of the ygap G between parts 2 'and `6". Caps 6" are mounted on casing 2" after the latter has been filled -with a pulverulent arc-quenching iiller 3", and solder laminate or solder sandwich generally indicated at 8" is inserted between the surface 6a of cap 6" and rims 2a. Solder laminate or solder sandwich 8" includes the inner layer 8a of fluxing agent and the outer layers 8b of soft solder, e.g. tin or an alloy of tin. After heating of cap 6" and fusion of solder laminate 8" Iand exertion of axial pressure on cap 6" the structure turns from that shown in FIG. 9 to that shown in FIG. 10. To be more specific, cap 6 is pressed downwardly while being heated, thus reducing the gap Width between surface 6a and the top surface of filler 3", and causing the excess of liquefied solder to ilow into gap G between surface 6b" and casing 2". After the solder apparent in the structure solidifies and hardens there is a layer of solder substantially coextensive with surface 6a of caps 6" establishing a solder joint between said surfaces 6a" and ribbon 1" at the points thereof engaging rims 2a". These layers 5 have projections 5a" extending in a direction longitudially of casing 2 into the gaps G formed between casing 2" and caps 6 establishing solder joints between surfaces 6b and the ends 1a of ribbon 1" on the outside of casing 2".

Tests made with fuses embodying this invention revealed a much greater uniformity of performance than that generally encountered with fuses having so-called blind solder joints between Kthe ends of the link and the terminal caps or ferrules. This is attribut-able to the fact that the joints 5, 5 and 5" are formed under pressure :at exactly the same point of the link or ribbon 1, 1, 1 so that the effective length of the link remains rigorously constant throughout a large number of fuses coming from Ia production line.

It will 4be understood that I have illustrated and described herein preferred embodiments of my invention, and that various alterations may be made in the details without departing from the spirit and scope of the invention as defined in Ithe appended claims.

I claim as my invention:

1. An electric fuse comprising a tubular casing of relatively resilient insulating material forming -a pair of rims at the axially outer ends thereof; an elongated fusible element formed by a length of perforated resilient sheet metal inserted into said casing, lsaid ribbon having points engaging angularly displaced points of said pair of rims and having .axially outer ends bent around said points of said pair of rims Ito the outer surface of said casing; a pair of metal 4caps having substantially liat circular inner end surfaces and substantially cylindrical inner lateral surfaces mounted under pressure upon said casing and closin-g said axially outer ends of said casing and pressing said ends of said rib-bon into said outer surface of said casing to form a pair of lateral cavities therein; solidified pools of soft solder substantially coextensive with said at inner surfaces of said pair of caps establishing solder joints between said surfaces and said ribbon `at said points thereof engaging said pair of rims; and said solidified pools of soft solder having projections extending in a direction longitudinally of said casing establishing solder joints between said inner lateral surface of said pair of caps and said ends of said ribbon situated in' said pair of lateral cavities, said projections being formed by solidified solder drawn by capillary action into said pair of lateral cavities.

2. An electric fuse as specified in claim 1 wherein said casing is made of an acrylonitrile-butadiene-styrene copolymer.

3. An electric fuse comprising a tubular casing of insulating material forming a pair of rims `at the axially outer ends thereof; a fusible element of a resilient sheet metal inserted into said casing, said element having an axially inner substantially cylindrical .portion Iand a pair of axially outer portions substantially in the shape of frustrated cones, said axially inner portion and said axially outer portions being `arranged in coaxial relation to said casing, said pair of axially outer portions having angularly displaced slots extending in a direction longitudinally of said casing and forming a plurality of angularly displaced terminal strips, said plurality of terminal strips engaging points of said pair of rims and having ends bent around said points of said pair of rims to the outer surface of said casing; a pair of metal caps having substantially iiat circular inner end surfaces and substantially cylindrical inner lateral surfaces closing said axially outer ends of said casing; layers of soft solder interposed between said fiat inner end surfaces of said pair of caps and said plurality of terminal strips at said points thereof engaging said pair of rims; land said layers having projections extending in a direction longitudinally of said casing into gaps lformed between said casing and said pair of caps and establishing solder joints between said ends of said plurality of terminal strips on said outer surface of said casing and said cylindrical lateral surfaces of said pair of caps.

4. An electric fuse comprising a tubular casing of insulating material forming :a pair of rims at the axially outer ends thereof; la substantially tubular fusible element of .a resilient sheet metal arranged in coaxial relation to and inside of said casing, said element including a substantially cylindrical axially inner portion and radially outwardly flaring axially outer portions, said axially outer Iportions including a plurality of angularly eq-uidistantly spaced terminal strips ldefining substantially V- shaped gaps therebetween, said terrnial strips having points engaging points of said pair of rims and having ends bent around said points of said pair of rims to the outer surface of said casing; a pair of metal caps having substantially flat circular inner end surfaces and substantially cylindricl inner lateral surfaces closing said axially outer ends 0f said casing; systems of substantially ciro'ularly arranged solder joints connecting said points of said plurality of terminal strips engaging points of said pair of rims with said flat circular inner end surfaces of said pair of caps; and additional systems of substantially circularly arranged solder joints connecting said ends of said plurality of terminal strips bent to the outer surface of said casing with said cylindrical inner lateral surfaces of said pair of caps.

References Cited in the file of this patent UNITED STATES PATENTS 1,702,062 Sonkin Feb. 12, 1929 1,861,369 Sundt May 31, l1932 2,090,220 Moor Aug. 17, 1937 2,680,1173 Hitchcock .Tune 1, 1954 2,832,868 Kozacka Apr. 29, 1958 FOREIGN PATENTS 580,759 Great Britain Sept. 18, 1946 

1. AN ELECTRIC FUSE COMPRISING A TUBULAR CASING OF RELATIVELY RESILIENT INSULATING MATERIAL FORMING A PAIR OF RIMS AT THE AXIALLY OUTER ENDS THEREOF; AN ELONGATED FUSIBLE ELEMENT FORMED BY A LENGTH OF PERFORATED RESILIENT SHEET METAL INSERTED INTO SAID CASING, SAID RIBBON HAVING POINTS ENGAGING ANGULARLY DISPLACED POINTS OF SAID PAIR OF RIMS AND HAVING AXIALLY OUTER ENDS BENT AROUND SAID POINTS OF SAID PAIR OF RIMS TO THE OUTER SURFACE OF SAID CASING; A PAIR OF METAL CAPS HAVING SUBSTANTIALLY FLAT CIRCULAR INNER END SURFACES AND SUBSTANTIALLY CYLINDRICAL INNER LATERAL SURFACES MOUNTED UNDER PRESSURE UPON SAID CASING AND CLOSING SAID AXIALLY OUTER ENDS OF SAID CASING AND PRESSING SAID ENDS OF SAID RIBBON INTO SAID OUTER SURFACE OF SAID CASING TO FORM A PAIR OF LATERAL CAVITIES THEREIN; SOLIDIFIED POOLS OF SOFT SOLDER SUBSTANTIALLY COEXTENSIVE WITH SAID FLAT INNER SURFACES OF SAID PAIR OF CAPS ESTABLISHING SOLDER JOINTS BETWEEN SAID SURFACES AND SAID RIBBON AT SAID POINTS THEREOF ENGAGING SAID PAIR OF RIMS; AND SAID SOLIDIFIED POOLS OF SOFT SOLDER HAVING PROJECTIONS EXTENDING IN A DIRECTION LONGITUDINALLY OF SAID CASING ESTABLISHING SOLDER JOINTS BETWEEN SAID INNER LATERAL SURFACE OF SAID PAIR OF CAPS AND SAID ENDS OF SAID RIBBON SITUATED IN SAID PAIR OF LATERAL CAVITIES, SAID PROJECTIONS BEING FORMED BY SOLIDIFIED SOLDER DRAWN BY CAPILLARY ACTION INTO SAID PAIR OF LATERAL CAVITIES. 